Plant gene transfer technology continues to progress in recent years, and has become a new way to improve varieties of crops. Scientists can put a particular gene, named foreign gene, into a plant so that the plant expresses traits which would not be expressed originally. The process which transfers foreign genes into organisms is known as gene transfer. In the past, scientists must go through a lengthy breeding process to transfer the special gene into cultivated species, and the parents with the special gene also must be able to hybrid with the cultivated species. On the contrary, gene transfer technology does not have these restrictions. Once transgenic technology is established successfully, new varieties of crops, which can not be bred well by traditional breeding, will be bred efficiently with improved ability to reduce losses or increase production per unit area. In a variety of plant gene transfer methods, the more commonly used are gene gun method, agrobacterium-mediated gene transfer method and electroporation method. Gene transfer methods applicable to different plant species and tissues are not the same. At present, transgenic tomato is produced by agrobacterium-mediated gene transfer method. The first genetically modified crop allowed in the market was launched in the United States in 1994, which was the genetically modified tomato with extended period of consumption. Because the gene transfer efficiency and the renewable capacity of tomatoes are better than that of most economic crops, tomatoes have been considered as a model of transgenic crops, and are widely used in various types of basic science research and application issues.
Gene expression is an important step in regulating cell physiology. The promoter used mostly for the gene expression in plant transformation is tobacco mosaic virus 35S promoter that is expressed generally in various tissues and developmental stages of a plant. Hence, tobacco mosaic virus 35S promoter is not suitable for the tissue specific gene expression. It is also not suitable while the general gene expression may cause damage to the plant. Applying a promoter with tissue specificity and developmental stage specificity may be a good solution for the above conditions.